This invention relates generally to focus control systems for use in cameras, video cameras and the like and more particularly to such a focus control system by which an automatic focus control or a manual control can selectively be effected.
Portable video camera devices in the recent years are normally provided with an automatic focus control function and a manual focus control function so that the user can selectively use the two functions at his wish. The focus control systems for such camera devices with the two functions are generally classified into the following two types. The first type is constructed such that a front lens group is driven by an output from an automatic focus control circuit while it can also be moved by a manual operation. In the second type, the focus control is effected by moving a master lens group which is disposed rearwardly of a zoom lens group.
A focus control system of the aforesaid first type is advantageous in that the focused state obtained by the front lens group is not affected when the zoom lens group behind the front lens group is moved to change the magnification factor, but has the problem that it is not possible to focus on a subject located very closely to the camera device body. A focus control system of the second type is advantageous in that it is possible to focus on a subject located up to very near (for example, 0.02 m before) the camera body, but is disadvantageous in the following. When the zoom lens group is moved, the master lens group must also be moved to compensate for the change of the focusing condition accompanied by the movement of the zoom lens group. In addition, since a very small movement of the master lens group brings about a significant change in the focusing condition, it is extremely difficult to manually operate the master lens group. In the manual mode of operation of the conventional focus control system of this type, the position of the master lens group is therefore electrically controlled within a movable range thereof based on an output from a variable resistor, a switch or the like which is manually operated, so that a virtual manual operation is performed. However, such a virtual manual operation is not natural for the user as compared to an actual manual operation.